JP7187954B2 - Evaluating Method of Delamination Resistance of Alumina-Magnesia Castable Refractories - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for evaluating spalling resistance of an alumina-magnesia castable refractory used as a lining furnace material for molten metal processing vessels.

Alumina-magnesia castable refractories used for molten steel ladles and the like have the problem of peeling wear due to cracks that occur during use. The main cause of cracks in alumina-magnesia castable refractories during use is considered to be buckling caused by volumetric expansion associated with the spinel formation reaction between alumina and magnesia, which are the constituent raw materials of the refractory.

In order to prevent buckling of alumina-magnesia castable refractories during use, the following two methods have been investigated. The first is a method of imparting softening under load to an alumina-magnesia castable refractory in order to relax the stress generated by the volume expansion associated with the spinel formation reaction between alumina and magnesia, which causes buckling. . The second point is a method of controlling the volume expansion associated with the spinel formation reaction between alumina and magnesia to reduce the stress generated by the volume expansion.

In Patent Documents 1 and 2, moderate load softening is imparted at a high temperature of 1400 ° C. or higher, where the volume expansion due to the spinel formation reaction between alumina and magnesia, which are the constituent raw materials of the alumina-magnesia castable refractory, increases. Alumina-magnesian castable refractories are disclosed.
In Patent Document 3, by adopting the residual linear change rate of the alumina-magnesia castable refractory after firing at 1500 ° C. for 3 hours in the air as a test method for volume expansion during use of the alumina-magnesia castable refractory, Disclosed is an alumina-magnesia castable refractory in which the volume expansion associated with the spinel formation reaction between alumina and magnesia during use is controlled.

JP-A-5-185202 JP-A-2001-253781 JP-A-9-30859

However, even if the alumina-magnesia castable refractories described in Patent Documents 1 to 3 are used, there is a problem in that peeling wear caused by cracks occurring in the castable refractories during use cannot be eliminated.

As a result of investigating the wear mechanism of alumina-magnesia castable refractories used in molten steel ladles, the present inventors found that cracks that occur in refractories during use, which causes peeling wear, are caused by alumina, which is a constituent raw material of refractories. It is not caused by buckling caused by volume expansion accompanying the spinel formation reaction between and magnesia, but a liquid phase generated by melting of the constituent materials of the refractory during use, and the formation of a solid from the liquid phase (precipitation) is involved. However, in the prior art, there was no method for evaluating the spallation resistance of alumina-magnesia castable refractories to determine whether spallation wear would occur due to cracks caused by the liquid phase generated during use.

An object of the present invention is to provide a method for evaluating spallation resistance of an alumina-magnesia castable refractory to determine whether spallation wear occurs due to cracks caused by a liquid phase generated during use.

As a result of intensive studies by the present inventors, in alumina-magnesia castable refractories in use, the liquid generated in the refractory structure in a high temperature state when in contact with molten steel and a relatively low temperature state after discharging molten steel The change in the amount of the phase/solid phase is correlated with the peel resistance, and the peel resistance can be grasped from the change in the coefficient of linear thermal expansion (also called "coefficient of linear expansion"). rice field.
That is, the gist of the present invention is as follows.
(1) A method for evaluating peel resistance of an alumina-magnesia castable refractory, wherein the castable refractory has a residual linear change rate of 0% or more after firing for 3 hours or more at 1400 ° C. or higher and 1600 ° C. or lower. , a step of heat-treating the castable refractory for 3 hours or more at a temperature T1 higher than the temperature at which the liquid phase of the castable refractory is generated; A step of measuring the linear thermal expansion coefficient of the castable refractory while increasing the temperature to, a step of measuring the linear thermal expansion coefficient of the castable refractory while cooling from the temperature T2 to room temperature, and a temperature of T1 or less A step of calculating a difference value between the linear thermal expansion coefficient in the temperature rising process and the linear thermal expansion coefficient in the cooling process at T3, and a step of judging peeling resistance from the difference value. Evaluation method for peeling resistance of castable refractories.
(2) The method for evaluating peeling resistance of a castable refractory according to (1), wherein the predetermined temperature T1 is a constant temperature selected from 1400 to 1500°C.
(3) The method for evaluating peeling resistance of a castable refractory according to (1), wherein the predetermined temperature T1 is 1400°C.
(4) The method for evaluating peel resistance of a castable refractory according to any one of (1) to (3), wherein the predetermined temperature T2 is a constant temperature selected from over 1400° C. and 1600° C. or less.
(5) The method for evaluating peel resistance of a castable refractory according to any one of (1) to (3), wherein the predetermined temperature T2 is 1500°C.
(6) The step of determining the peeling resistance determines the maximum value of the difference between the temperature at which the liquid phase of the castable refractory after the heat treatment completes precipitation into the solid phase and the temperature T1. , wherein the peel resistance is determined by comparing the maximum value with a predetermined target value and determining whether the maximum value is equal to or less than the target value (1) to (5) ) The method for evaluating the peel resistance of the castable refractory according to any one of ).
(7) The method for evaluating peel resistance of a castable refractory according to any one of (1) to (5), wherein the predetermined temperature T3 is a constant temperature selected from 1200 to 1400°C.
(8) The method for evaluating peel resistance of a castable refractory according to any one of (1) to (5), wherein the predetermined temperature T3 is 1200°C.
(9) The method for evaluating the peeling resistance of a castable refractory according to (8), wherein the castable refractory having the difference value of 0.1% or less is judged to have high peeling resistance.

According to the present invention, it is possible to accurately evaluate the spallation resistance of an alumina-magnesia castable refractory, ie, whether or not spallation wear occurs due to cracks caused by a liquid phase generated during use.

1 is a conceptual diagram of linear thermal expansion coefficient curves of an alumina-magnesia castable refractory after sintering at 1400° C. during the heating process from room temperature to 1600° C. and the cooling process from 1600° C. to room temperature. 1 is a diagram showing the results of measurement of linear thermal expansion coefficients in the temperature rising process from room temperature to 1500° C. and the cooling process from 1500° C. to room temperature in Test Example 1. FIG.

Since the alumina-magnesia castable refractories to which the evaluation method according to the present invention is applied are mainly used in molten steel ladles, the case of using them in molten steel ladles will be described below as an example. The same can be applied when used for other containers.

A molten steel ladle is a molten metal processing vessel that conveys molten steel tapped from a converter to a continuous casting machine. Therefore, the alumina-magnesia castable refractory used for the molten steel ladle is heated during the period when the molten steel is retained, and the molten steel does not exist in the ladle from the completion of casting to the start of receiving steel in the converter. The period will be cooled. That is, alumina-magnesia castable refractories are used in an environment where heating and cooling are repeated.

In alumina-magnesia castable refractories used in such environments, spalling damage caused by cracks occurs after the temperature distribution inside the refractory reaches a steady state. According to steady state heat transfer calculation inside the refractory in use, it was found that the position where the crack occurred was the position where the temperature reached about 1400°C.

By the way, alumina-magnesia castable refractories are composed of refractory raw materials such as alumina cement having alumina, magnesia, silica, and CaO.Al ₂ O ₃ as main crystal phases. In a region where the temperature inside the refractory is 1400° C. or higher, these refractory raw materials are considered to cause the following reaction (1).

That is, the refractory raw material reacts during use, and at 1400° C. or higher, CaO 6Al is produced from the reaction of alumina cement and part of alumina in addition to spinel produced from the reaction of magnesia and part of alumina. A liquid phase is formed from the reaction of ₂ O ₃ and silica with other oxides. The amount of spinel, CaO.6Al ₂ O ₃ and liquid phase produced in the reaction of formula (1) depends on the content of the refractory raw material contained in the alumina-magnesia castable refractory. As the temperature rises, the amount of liquid phase produced increases.

Next, the behavior of the microstructure of the alumina-magnesia castable refractory in the molten steel ladle during use is speculated. After receiving the first steel, during the period in which the molten steel is retained, a liquid phase is generated based on the reaction of formula (1) in the region where the temperature inside the refractory becomes 1400°C or higher, and the refractory in contact with the molten steel at approximately 1600°C. In terms of product operation, the amount of liquid phase produced is maximized. When the liquid phase is generated, the refractory shrinks due to the capillary force of the liquid phase. That is, during use, the structure of the refractory shrinks due to the liquid phase that is generated from the region of 1400° C. inside the refractory to the operating surface of the refractory in contact with the molten steel. As the amount of liquid phase generated inside the refractory during use increases, the amount of contraction of the structure of the refractory increases.

Next, the reaction of the following formula (2) proceeds during the period after the casting is completed, in which the molten steel does not exist in the ladle, that is, during the period in which the refractory is cooled.

That is, during the cooling process, solid phases such as CaO.6Al ₂ O ₃ and CaO--MgO--SiO ₂ --Al ₂ O ₃ based compounds are precipitated from the liquid phase.
The reaction of formula (1) occurs irreversibly when the temperature reaches 1400° C. or higher. On the other hand, the reaction of formula (2) occurs reversibly in response to temperature changes in tissue once subjected to a heat history of 1400° C. or higher. That is, in the region where exfoliation wear occurs during use of the molten steel ladle, the irreversible reaction of formula (1) and the reversible reaction of formula (2) occur.

As a result of detailed investigation of the precipitation phenomenon of the solid phase from the liquid phase during the cooling process using a phase diagram, the inventors of the present invention presumed that different components are precipitated stepwise as follows.

First, the CaO.6Al ₂ O ₃ component from the liquid phase precipitates on the surface of the CaO.6Al ₂ O ₃ particles that are present in an unmelted state, and the particle diameter of the CaO.6Al ₂ O ₃ particles increases. Causes volume expansion (first precipitation process). Subsequently, the CaO—MgO—SiO ₂ —Al ₂ O ₃ -based compound precipitates from the remaining liquid phase between particles already present as a solid phase, thereby completing the precipitation of the solid phase from the liquid phase (Second second precipitation process). When the CaO--MgO-- _SiO.sub.2 --Al.sub.2O.sub.3 _- based compound precipitates from the liquid phase _, the volume decreases due to the density difference between the two. The refractory expands in the first precipitation process, and the expansion coefficient is the largest around 1200° C. where all the _{CaO.6Al 2} O components precipitate.

Next, the thermal expansion and contraction behavior of the refractory which is heated up to about 1600° C. and repeatedly heated and cooled during use is estimated.

Figure 1 shows continuous line heating during the heating process from room temperature to 1600°C and the cooling process from 1600°C to room temperature for the alumina-magnesia castable refractory that was heat-treated at 1400°C for 3 hours in the air. FIG. 2 shows a conceptual diagram of an expansion curve.

In the alumina-magnesia castable refractory heat-treated at 1400 ° C. for 3 hours, the reactions of the above formulas (1) and (2) occur, so at room temperature, alumina, spinel, CaO.6Al ₂ O ₃ , and CaO--MgO--SiO ₂ --Al ₂ O ₃ -based compounds.

In the temperature rising process from room temperature to 1600° C., only expansion of these solids occurs up to about 1200° C. (process O→A). In the process of further raising the temperature from 1200° C. to 1600° C. (process A→B), CaO.6Al ₂ O ₃ and CaO—MgO—SiO ₂ —Al ₂ O ₃ based compounds melt and a liquid phase begins to form. As the temperature rises, the amount of liquid phase produced increases, and the refractory shrinks due to the production of the liquid phase as described above. The refractory working surface, whose temperature reaches 1600° C., as in the case of receiving molten steel, shrinks the most due to the reduction of solid phase and the formation of liquid phase.

Subsequently, when the refractory is cooled to about 1200° C. (process B→C→D), like when molten steel is discharged from a ladle, CaO.6Al ₂ O ₃ precipitates from the liquid phase. and the _second precipitation process in which the CaO--MgO-- _SiO.sub.2 --Al.sub.2O.sub.3 _- based compound is precipitated, the volume of the refractory structure near the working surface expands. If the ladle receives molten steel again during the process B→C→D, the precipitated solid phase returns to the liquid phase and shrinks (process D→C→B).

The above is the behavior of the alumina-magnesia castable refractory heat-treated at 1400° C. for 3 hours, and the thermal expansion and contraction behavior of the working surface side subjected to a heat history of 1400° C. or higher during use.

On the other hand, in the part where the temperature does not reach 1400 ° C. or higher during use, the reaction of the above formula (1) does not occur, and even if the temperature reaches 1200 ° C. in FIG. Expansion of the feedstock continues (process A→B'). That is, the portion that has not reached 1400° C. or higher shows the linear thermal expansion coefficient in the process A→B′, while the portion that has reached 1400° C. or higher shows the linear thermal expansion coefficient in the process B→C→D. . Since stress relaxation is not a little caused by the liquid phase at the part where the temperature rises to 1400° C. or higher during use, peeling wear occurs at the part where the temperature is 1200° C. to 1400° C. as shown in FIG.

In this way, the alumina-magnesia castable refractory repeats the process of composition change and volume reduction due to melting of the refractory near the operating surface during use, and volume increase due to precipitation from the liquid phase to the solid phase, and the refractory structure Thermal expansion with the inside becomes discontinuous, strain is accumulated in the vicinity of the position reaching about 1400° C., which is the boundary, and cracks that cause peeling wear occur.

(Peeling resistance evaluation object)
Alumina-magnesia castable refractories to which the evaluation method according to the present invention is applied have a residual line change rate of 0% or more after firing at 1400° C. or higher and 1600° C. or lower for 3 hours or longer. As a test method for the residual linear change rate, it is preferable to use JIS-R2554 "Test method for linear change rate of castable refractories". Although the method does not specify the sintering temperature and sintering time, the present invention recommends a temperature of 1600° C. for 3 hours or longer.

In general, alumina-magnesia castable refractories preferably have moderate residual expansion after being subjected to heat history. A refractory with residual shrinkage, ie, a residual linear change rate of less than 0%, has dimensions after being heated and cooled that are smaller than the original dimensions before heating. A refractory with a residual linear change rate of less than 0% near 1400 ° C. is clearly cracked during use, and often has poor peeling resistance in the first place, so it cannot be used for the production of actual equipment. . Therefore, the present invention is applied to an alumina-magnesia castable refractory having positive residual expansion, in other words, having no residual shrinkage.

Alumina-magnesia castable refractories are fired at temperatures up to 1600° C., as they can be heated up to 1600° C. on the working surface in contact with molten steel during use. Considering the time during which the molten steel is exposed to about 1600° C., firing for 3 hours or more is sufficient. Therefore, the present invention is applied to an alumina-magnesia castable refractory that has a residual linear change rate of 0% or more when heated at a temperature of 1400° C. or more and 1600° C. or less for 3 hours or more, that is, does not shrink.

(Heat treatment process for castable refractories)
In the present invention, first, for the alumina-magnesia castable refractory to be evaluated, at a temperature higher than the temperature at which the liquid phase of the castable refractory is generated (this temperature is defined as "predetermined temperature T1") Heat for at least 3 hours.

The reason why the heat treatment is performed in advance at the predetermined temperature T1 for 3 hours or more is to cause the reaction of the formula (1). The reaction of formula (1) occurs irreversibly at about 1400° C. or higher. Even if the evaluation method according to the present invention is performed on a refractory that has not been subjected to the heat treatment, it is not possible to perform an appropriate delamination resistance evaluation. This is because the portion of the refractory heated to 1400° C. or higher in the actual use environment repeats expansion and contraction due to the reaction of formula (2) after the initial reaction of formula (1) occurs. This is because the thermal expansion behavior of the refractory after completion of the reaction of formula (1) affects the peeling resistance.

The predetermined temperature T1 may be any temperature at which the reaction of formula (1) proceeds, but is preferably a constant temperature selected from 1400 to 1500.degree. More preferably the temperature is as close as possible to 1400°C. The reason why the heat treatment time is 3 hours or more is to allow the reaction of the formula (1) to reach equilibrium. By using a test piece heat-treated at 1400° C. for 3 hours or longer, it is possible to reproduce the thermal expansion behavior of a refractory in use.

Depending on the material of the alumina-magnesia castable refractory, the more the heat treatment temperature exceeds 1400 ° C., the more the amount of liquid phase produced in the reaction of the above formula (1) becomes excessive, and the liquid phase sintering between the raw material particles Densification of the refractory structure may occur with the formation of strong bonds. When measuring the linear thermal expansion coefficient of such a refractory in which strong bonds are formed between the raw material particles, even if a liquid phase is generated during the heating process, the The volume expansion that occurs during the precipitation of CaO.6Al ₂ O ₃ from the liquid phase in the cooling process up to the temperature of 100° C. is suppressed. As a result, in the cooling process, the value of the coefficient of linear thermal expansion measured in the temperature range equal to or lower than the predetermined temperature T1 may not appropriately reflect changes in the state of the refractory structure in the actual use environment. Therefore, in the present invention, although the predetermined temperature T1 can be selected depending on the refractory, 1400°C is most preferable, and 1400°C is sufficiently applicable.

(Measuring process of linear thermal expansion coefficient in heating process and cooling process between room temperature and predetermined temperature T2)
The linear thermal expansion coefficient of the alumina-magnesia castable refractory that has undergone the heat treatment step is measured while the temperature is raised from room temperature to a predetermined temperature T2 (T2>T1). Incidentally, the predetermined temperature T2 is set higher than the temperature T1 in order to advance the reverse reaction of the formula (2). After the temperature rise, the linear thermal expansion coefficient is measured while cooling from the predetermined temperature T2 to room temperature.

The predetermined temperature T2 is the maximum attainable temperature of the linear thermal expansion coefficient measurement temperature, and is a temperature at which the equilibrium state reached in the heat treatment step can be achieved, and it is sufficient that it is within the range of the molten steel temperature at the maximum. The predetermined temperature T2 is preferably a constant temperature selected from over 1400° C. and 1600° C. or less. More preferably it is 1500°C.

Assuming that the predetermined temperature T2 is 1500° C., it is possible to use a testing apparatus capable of conducting a thermal expansion test of refractories in accordance with the widely used JIS-R2207-1. In addition, if the temperature is raised to 1500°C, a liquid phase is generated and stress relaxation occurs, so it is possible to evaluate the peeling resistance without raising the temperature to about 1600°C which is the molten steel temperature.

A method for testing the coefficient of linear thermal expansion used in the present invention is not particularly limited as long as the coefficient of linear thermal expansion can be measured from room temperature to a predetermined temperature T2. As will be described later, when obtaining the maximum value of the difference between the coefficient of linear thermal expansion during the heating process and the coefficient of linear thermal expansion during the cooling process, the coefficient of linear thermal expansion from room temperature to the predetermined temperature T1 is measured over time. It is preferable to be able to measure It is preferable to use a test piece and test conditions conforming to JIS-R2207 "Testing method for thermal expansion of refractories" because it is easy to compare with conventional evaluation results and physical property values. More preferably, JIS-R2207-1 "non-contact method" is used, which has little effect on the expansion and contraction of the liquid phase.

(Calculation of the difference value between the linear thermal expansion coefficient during the heating process and the linear thermal expansion coefficient during the cooling process)
In the present invention, the difference between the linear thermal expansion coefficient during the temperature rising process and the linear thermal expansion coefficient during the cooling process at a temperature equal to or lower than the predetermined temperature T1 (this temperature is defined as "predetermined temperature T3") including the step of calculating the value. As mentioned above, peeling is caused by distortion caused by the discontinuity of the linear thermal expansion coefficient between the working surface of the refractory and the inside. , the temperature at which the first precipitation process is completed, for example, 1200° C. or higher.

In the refractory to be evaluated by the evaluation method according to the present invention, when the temperature rises to 1200 ° C. or higher in the linear thermal expansion coefficient measurement step, a liquid phase begins to form, and the linear thermal expansion coefficient decreases. The differential thermal expansion during the formation of the liquid phase, which is minimized at temperature T2, causes less strain due to stress relaxation. In the subsequent cooling process, expansion occurs due to crystal precipitation, and the coefficient of linear thermal expansion reaches the maximum at 1200°C.

On the other hand, as described above, in a region where the heat history is less than the temperature at which the irreversible reaction of formula (1) occurs, for example, less than 1400 ° C. of the refractory in actual use, the temperature is 1200 ° C. or higher. However, the liquid phase does not form until it is heated to 1400°C or higher, and its thermal expansion behavior shows that it remains in the solid phase up to 1400°C. Therefore, it is up to about 1400° C. that distortion occurs due to the difference in coefficient of linear thermal expansion. Therefore, the predetermined temperature T3 should be set to a temperature range from the temperature at which the first precipitation process is completed to the temperature at which the irreversible reaction of formula (1) occurs. Specifically, the predetermined temperature T3 is a temperature range from a temperature at which precipitation of the liquid phase of the castable refractory after the heat treatment at the predetermined temperature T1 to the solid phase is completed to the predetermined temperature T1, or A constant temperature selected from 1200 to 1400° C. is preferred.

Furthermore, the difference value of the linear thermal expansion coefficient between the part near the working surface that has received a thermal history of 1400 ° C. or higher and the part that has received only a thermal history of 1400 ° C. or less in the refractory is between 1200 and 1400 ° C. is considered to be maximum at 1200°C. Since it is considered that the larger the difference value, the larger the strain, the greater the effect on delamination. Therefore, in the present invention, it is recommended to judge the delamination resistance by the differential value of the coefficient of linear thermal expansion when the predetermined temperature T3 is 1200°C. Regarding the difference value, it depends on the material of the refractory material, the pre-sintering temperature, and the usage environment, and the numerical value that is most correlated with the releasability may be used.

(Detachment resistance judgment process)
The present invention includes a step of judging peel resistance from the difference value. This step determines the maximum value of the absolute values of the difference values, compares the maximum value with a target value, and judges peel resistance by determining whether the maximum value is equal to or less than the target value. It is done by The target value can be appropriately set in advance. For example, if the difference value is 0.1% or less when the predetermined temperature T3 is 1200° C., it may be determined that the peeling resistance is high. .

As a result of intensive investigation by the inventors, it was found that at 1200°C, almost no liquid phase was generated during the heating process and cooling process, and that the difference in coefficient of linear thermal expansion was maximum within the operating temperature range (up to 1600°C). Therefore, a good correlation is obtained with the presence or absence of peeling wear of the alumina-magnesia castable refractory. Especially when the difference value is 0.1% or less when used in a ladle, the peeling resistance is remarkable. It was found that the

(Composition of alumina-magnesia castable refractory raw material)
The evaluation object of the evaluation method according to the present invention can be produced, for example, by using materials having the following compositions as raw materials. However, the evaluation object of the evaluation method according to the present invention is an alumina-magnesia castable refractory, and if the residual linear change rate after firing at a temperature of 1400 ° C. or more and 1600 ° C. or less for 3 hours or more is 0% or more , the composition of which is not limited to the following examples.

Alumina used for the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention includes sintered alumina, electrofused alumina, heavy burnt alumina, calcined alumina, bauxite, electrofused bauxite, and clay. Shale or the like can be used. As for the particle size of alumina, a general one having a maximum particle size of less than 10 mm can be used. The blending ratio of alumina is desirably in the range of 78% to 93.5% by mass in the total amount of the alumina-magnesia castable refractory.

Sintered magnesia or electrofused magnesia can be used as the magnesia used for the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention. As the particle size of magnesia, a general one having a maximum particle size of less than 1 mm can be used. The blending ratio of magnesia is desirably in the range of 3% to 10% by mass in the total amount of the alumina-magnesia castable refractory.

The silica used in the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention includes silica such as silica flour and silica fume that are by-produced during the production of silicon and silicon alloys, and silica such as silica by the vapor phase method. aerosol-like silica produced in and dried amorphous hydrous silica synthesized by a wet method can be used. The particle size of silica is desirably 1 μm or less. The blending ratio of silica is desirably in the range of 0.5% to 2% by mass in the total amount of the alumina-magnesia castable refractory.

Alumina cement containing CaO.Al ₂ O ₃ can be used as the alumina cement used for the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention. Alumina cement containing alumina or spinel other than CaO.Al ₂ O ₃ may be used. The blending ratio of the alumina cement is desirably in the range of 3% to 10% by mass in the total amount of the alumina-magnesia castable refractory.

Generally used dispersants may be used for the alumina-magnesia castable refractories to be evaluated by the evaluation method according to the present invention. For example, sodium tripolyphosphate, sodium hexametaphosphate, acidic sodium hexametaphosphate, sodium polyacrylate, sodium sulfonate, sodium naphthalenesulfonate, sodium lignosulfonate, ultrasodium polyphosphate, sodium carbonate, sodium borate, sodium citrate, etc. Available. The blending ratio of the dispersant may also be a general prescription. For example, a range of 0.03% to 0.1% in terms of outer coating is desirable with respect to 100% by mass of the alumina-magnesia castable refractory.

As the explosion prevention agent used for the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention, a commonly used one may be used. For example, vinylon fiber, aluminum lactate, metal aluminum as a foaming agent, and azodicarbonamide can be used. The blending ratio of the explosion-proof agent may also be a general prescription. For example, a range of 0.01 to 0.03% in terms of outer coating is desirable with respect to 100% by mass of the alumina-magnesia castable refractory.

(Preparation of test piece to be evaluated)
It is preferable that the preparation of the alumina-magnesia castable refractory test piece used for carrying out the evaluation method according to the present invention is carried out under conditions as similar as possible to those in the actual equipment. However, the method for producing the test piece is not particularly limited as long as the test piece produced has a residual linear change rate of 0% or more after baking at 1400° C. or more and 1600° C. or less for 3 hours or more.

For example, it may be produced by adding 4 to 8% by mass of water to 100% by mass of the refractory raw material satisfying the above composition, kneading it with a mixer, and pouring it into a mold. In order to improve filling properties during production, vibration may be imparted to the mold into which the kneaded material is poured.

Test examples of the present invention and reference examples thereof are shown below.

Table 1 shows the composition of raw materials for the alumina-magnesia castable refractories and the evaluation results. To the castable refractory produced with the composition shown in Table 1, sodium polyacrylate is added as a dispersant in the range of 0.06% to 0.1% by mass relative to the amount of refractory material, and water is added to the amount of refractory material. The mixture was added in an amount of 5 to 6.5% by mass, kneaded for 3 minutes using a twin-screw mixer, and the kneaded product was poured into a metal frame of a predetermined size while being vibrated. Then, after curing at room temperature for 24 hours, an evaluation sample was prepared by drying at 110° C. for 24 hours.

As a reference example of conventional peel resistance evaluation, the residual line change rate after firing at 1500° C. for 3 hours (h) was measured. The residual linear change rate was measured using the JIS-R2554 linear change rate test method for castable refractories.

In the present invention, the linear thermal expansion curve of the alumina-magnesia castable refractory was measured in accordance with the JIS-R2207-1 test method for thermal expansion of refractories. The test piece was previously heat-treated at a predetermined temperature T1 of 1400° C. for 3 hours. Continuously measure the linear thermal expansion coefficient of the test piece during the heating process from room temperature to a predetermined temperature T2 of 1500 ° C. and the cooling process from 1500 ° C. to room temperature. read the coefficient of linear thermal expansion at 1200°C.

On the other hand, the wear rate during actual use is 0.06% by mass to 0.06% by mass to 0.06% by mass of the alumina-magnesia castable refractory material with sodium polyacrylate as a dispersant based on the amount of the refractory material. Add water in the range of 1% by mass, further add water in the range of 5 to 6.5% by mass based on the amount of refractory material, knead for 3 minutes using a twin-screw mixer, and the kneaded product has a capacity of 300 tons. It is applied to the side wall of the molten steel ladle, and the thickness of the refractory is measured after using the molten steel ladle 70 times (ch), and the average wear rate is obtained by dividing the value subtracted from the original thickness by the number of times of use. (mm/ch). At the same time, the state of peeling wear due to cracks during use was visually observed.

FIG. 2 shows the results of continuously measuring the coefficient of linear thermal expansion in the temperature rising process from room temperature to a predetermined temperature T2 of 1500° C. and in the cooling process from 1500° C. to room temperature. It can be seen that the difference value of the coefficient of linear thermal expansion is 0.1% or less when the predetermined temperature T3 is 1200° C. in the cooling process and the heating process.

The castable refractories of Test Examples 1 to 3 had a relatively small residual linear change rate after firing at 1500° C. for 3 hours. Then, since the residual line change rate after firing at 1600°C for 3 hours was a positive value, the test piece that had been heat-treated at 1400°C for 3 hours in the air had a cooling process from 1500°C to room temperature and a The coefficient of linear thermal expansion was measured during the temperature rising process. The difference in linear thermal expansion coefficient at 1200° C. between the two processes was 0.1% or less, and it was judged that the peeling resistance was high. As a result of actual use, no peeling wear occurred during actual use, and the wear rate was relatively small, so the peeling resistance of the refractory could be accurately evaluated.

In Test Example 4, the residual line change rate after baking at 1500° C. for 3 hours is relatively large compared to Test Examples 1 to 3, and there was a concern about peeling loss from conventional experience. However, the residual line change rate after firing at 1600° C. for 3 hours was a positive value. Subsequently, when the linear thermal expansion coefficient of the present invention was measured, the differential value of the linear thermal expansion coefficient at 1200° C. was 0.1% or less, and it was judged that the peeling resistance was high. When the refractory was actually used, no peeling wear was observed, and the wear rate was almost the same as in Test Examples 1 to 3. Therefore, the peeling resistance of the refractory could be accurately evaluated.

In Test Examples 5 and 6, the value of the residual linear change rate after baking at 1500° C. for 3 hours was relatively low. The value of the residual line change rate after firing at 1600° C. for 3 hours also showed a positive value, though small. However, in the linear thermal expansion curve of the test piece heat-treated at 1400 ° C. for 3 hours in the air, the linear thermal expansion coefficient at 1200 ° C. in the cooling process from 1500 ° C. to room temperature and the temperature rise from room temperature to 1500 ° C. The differential value of the coefficient of linear thermal expansion at 1200° C. in the process exceeded 0.1%, and it was judged that the peeling resistance was poor. As a result of the actual machine test, peeling wear occurred and the wear rate increased. Therefore, it was possible to accurately evaluate the peeling resistance of the refractory.

Reference Example 1 has a low residual linear change rate after sintering at 1500° C. for 3 hours, and is a refractory with a slightly low residual expansibility, although it is expected that there is not much concern about peeling from conventional experience. Therefore, when the residual linear change rate after firing at 1600° C. for 3 hours was measured, it was found to be a negative value. Generally, such refractories are not used in actual equipment. As a reference, in the test piece that was subjected to heat treatment at 1400 ° C. in the atmosphere for 3 hours, which corresponds to the present invention, the coefficient of linear thermal expansion at 1200 ° C. in the cooling process from 1500 ° C. to room temperature and the rise from room temperature to 1500 ° C. When the coefficient of linear thermal expansion was measured at 1200°C during the temperature process, the difference was 0.1% or less. However, when an actual machine test was conducted, peeling wear was observed, and the wear rate was high. As described above, the castable refractory that has a negative residual linear change rate after firing at 1600° C. for 3 hours, that is, the castable refractory that shrinks remains even if the difference value of the linear thermal expansion coefficient is small. It may not be suitable for use as a lining furnace material for a metal processing vessel.

According to the present invention, before constructing an actual machine, using a test piece of the alumina-magnesia castable refractory to be used, the peeling resistance of the alumina-magnesia castable refractory can be accurately evaluated. can. Therefore, by using the evaluation method according to the present invention, it is possible to compare and study the peeling resistance of various castable refractories, and to find an alumina-magnesia castable refractory with extremely excellent durability and the castable refractory. It is possible to manufacture the actual machine used.

Claims (7)

Alumina-magnesia castable refractory evaluation method for peeling resistance,
The castable refractory has a residual line change rate of 0% or more after firing at 1400 ° C. or higher and 1600 ° C. or lower for 3 hours or more,
A step of heat-treating the castable refractory for 3 hours or more at a temperature T1 higher than the temperature at which the liquid phase of the castable refractory is generated;
A step of measuring the linear thermal expansion coefficient of the castable refractory while raising the temperature of the castable refractory after the heat treatment from room temperature to a temperature T2 higher than the temperature T1; A step of measuring the linear thermal expansion coefficient of the castable refractory;
a step of calculating a difference value between the linear thermal expansion coefficient in the heating process and the linear thermal expansion coefficient in the cooling process at a temperature T3 that is equal to or lower than T1;
A step of judging the peel resistance from the difference value;
with
The temperature T3 is 1200° C.,
A method for evaluating peeling resistance of a castable refractory , wherein the castable refractory having a difference value of 0.1% or less is judged to have high peeling resistance. The method for evaluating peeling resistance of a castable refractory according to claim 1, wherein the temperature T1 is a constant temperature selected from 1400 to 1500°C. 2. A method for evaluating peeling resistance of a castable refractory according to claim 1, wherein said temperature T1 is 1400[deg.]C. The method for evaluating peeling resistance of a castable refractory according to any one of claims 1 to 3, wherein the temperature T2 is a constant temperature selected from over 1400°C and 1600°C or less. The method for evaluating peel resistance of a castable refractory according to any one of claims 1 to 3, wherein the temperature T2 is 1500°C. The step of determining the peeling resistance includes determining the maximum value of the difference between the temperature T1 and the temperature at which the liquid phase of the castable refractory after the heat treatment completes precipitation into the solid phase, and determining the maximum 6. The peel resistance is determined by comparing the value with a predetermined target value and determining whether the maximum value is equal to or less than the target value. A method for evaluating the peeling resistance of the castable refractory described in the paragraph. The method for evaluating peeling resistance of a castable refractory according to any one of claims 1 to 5, wherein the temperature T3 is a constant temperature selected from 1200 to 1400°C.

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